Slow Temperature Rise Research Articles

Climate variability in the SE Alps of Italy over the past 17 000 years reconstructed from a stalagmite record

Stalagmite SV1 from Grotta Savi, located at the SE margin of the European Alps (Italy), is the first Alpine speleothem that continuously spans the past c. 17kyr. Extension rate and δ18Oc record for the Lateglacial probably reflect a combination of temperature and rainfall, with rainfall exerting the dominant effect. Low speleothem calcite δ18 Oc values were recorded from c. 14.5 and 12.35 kyr, during GI-1 (Bølling— Allerød) interstadial, which in our interpretation, was warm and wet. The GS-1 (Younger Dryas) was characterized by a shift to heavier δ18 Oc, coinciding with δ13Cc enrichment and extremely low extension rate (<8 μm/year). These characteristics indicate that GS-1 climate was cool and dry in the SE Alps. Calibration using historical data revealed that there is a positive δ18Oc/dT relationship. A 1°C rise in mean annual temperature should correspond to c. 2.85% increase of SV-1 δc18Oc. We reconstructed a slow and steady temperature rise of c. 0.5°C since 10 kyr BP, in broad agreement with reconstructions from pollen data for SE Europe. Stalagmite SV1 indicates that climate variability in the SE Alps has been influenced by the Mediterranean Sea for the past c. 17 kyr.

Abrupt Climate Change: Inevitable Surprises

Climate change is now well recognized as a potentially significant factor in the human future, affecting ecological systems, agriculture, health, and settlement patterns. The scientific consensus, periodically assessed by the Intergovernmental Panel on Climate Change, foresees a long‐term atmospheric warming of a few degrees over a century. The accumulating knowledge of the world's climate history, however, suggests that any implied stability of trend may be illusory. The evidence comes from ice and seabed cores and tree rings, which can yield year‐by‐year information on atmospheric conditions and time‐series of mean temperatures extending back for millennia. These data show many episodes of a sudden rise or fall in temperature in particular regions, sometimes of 10°C or more in ten years, with the new mean lasting for decades or centuries. There is thus the likelihood—even the inevitability—of comparably large and abrupt changes occurring in coming years, a very different prospect from the “greenhouse warming” scenario projected by current large‐scale climate models. Moreover, the two phenomena may be connected: a continued slow temperature rise may at some point trigger an abrupt shift in climate regime through mechanisms such as the effect on ocean circulation. In 2002 a committee set up by the US National Research Council reviewed what is known about this subject in a report, Abrupt Climate Change: Inevitable Surprises (Washington, DC: National Academy Press). The Council is the operating arm of the US National Academy of Sciences; the Committee on Abrupt Climate Change comprised mostly oceanographers and climate experts and was chaired by Richard B. Alley, Professor of Geosciences, Pennsylvania State University, a glaciologist and author of The Two‐Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future (Princeton, 2000).A recent spate of media attention to the subject has been occasioned less by the NRC report itself than by a dramatic scenario exercise derived from it, prepared under US Defense Department auspices, and by release of a disaster film with an instant‐ice‐age theme. The Pentagon study, An Abrupt Climate Change Scenario and Its Implications for United States National Security, authored by Peter Schwartz and Doug Randall, was issued in October 2003. It explores the hypothetical geopolitical consequences of a repetition in the near future of an event experienced 8,200 years ago (as recorded in an ice core from central Greenland): a sudden cooling of some 2–3° C, lasting for a century, punctuating climatic conditions broadly similar to those of the present day. In the scenario, the collapse of ocean heat‐conveying currents causes rapid cooling in the northern hemisphere and warming in the southern hemisphere. Outcomes include resource wars, large population movements, and “a significant drop in the human carrying capacity of the Earth's environment.”In February 2004 the NRC reasserted the more measured voices of its committee by issuing a four‐page summary of the 2002 report, under the same title as the full document. This “report in brief” is reproduced below.

Transfer of heat and moisture during oven baking of potatoes

AbstractPotatoes were baked for up to 60 min in a conventional fan‐assisted oven. Temperature profiles within the potato tubers were determined both by direct measurement and by following the inward progress of starch gelatinisation, which occurs at 65 °C. Temperature profiles with time were S‐shaped and about 30 min was needed for the centre to reach 100 °C. From the nature of the temperature profiles, long potato tubers will cook faster than round tubers of the same weight, and a varietal ‘shape factor’ was defined to quantify this effect. The slow temperature rise, compared to other forms of cooking, was due to evaporative cooling. Moisture loss was linear with time after an initial lag and reached 15–20% of the mass of the potato after 1 h of cooking. Approximately half of the moisture was lost from the outermost layer of the potato under the periderm, leaving behind a dried layer of flesh that appeared to restrict water transport and, unlike any other part of the potato, could exceed 100 °C. This has consequences for the thermal development of flavour compounds as well as for perceived texture.© 2002 Society of Chemical Industry

Contact heat evoked potentials as a valid means to study nociceptive pathways in human subjects

Contact heat evoked potentials (CHEPs) have been difficult to elicit due to slow temperature rise times. A recently developed heat-foil technology was used to elicit pain and CHEPs. Two groups of subjects were separately stimulated at the left arm with contact heat via one fast-acting (70°C/s) heat-foil thermode. A set of CHEPs was recorded, each at three subjective intensities: warm; slight; and moderate pain. In CHEPs, the 3D topography exhibited four components: T3–T4/N450; Cz/N550; Cz/P750; and Pz/P1000. A vertex topography map was observed in the late Cz/N550–Cz/P750 and parietal topography in the very-late Pz/P1000 components. Consistent statistical values in the peak latencies and amplitudes were noted between consecutive investigations. The correlation between the pain intensity ratings and the major Cz/P750 amplitudes was highly significant in each study. Our validity tests suggested CHEPs to be useful for research and clinical applications in studying human pain activation related to thermal and nociceptive pathways.

The branched - chain explosion time and slow temperature rise for homogeneous reactive system

This paper describes an investigation of the explosion time for an extended model involving a four stem mechanism. Significant deviations from past results were obtained leading to the fresh determination of criticality of a certain parameter δ and explosion times for which the results of calculations agree well with those obtained previously. The boundary between the explosion and slow temperature region is found.

‘Climate’ for social assessment: Experts, uncertainty and policy development

Policy‐makers often face the dilemma whether or not to include unwelcome findings in a policy process. The paper starts with a recent example of the interaction between research and policy‐making: the complex problem of greenhouse gases. Research has demonstrated a relationship between a slow rise in temperature on earth, the rise of CO2 in the atmosphere and societal circumstances. The author argues that what are usually seen as ‘social’ facts are actually based on politically charged assumptions. The example allows us to point out new aspects of the relationship between scientific research and policy development. These aspects are discussed in the light of recent literature: (a) political and systemic uncertainty; (b) dynamics and interaction of social‐scientific research and politics; (c) experts, their knowledge production and their acting as mediators.

High enthalpy extraction experiments with Fuji-1 MHD blow-down facility

Recent experimental results of closed cycle MHD electrical power generation with the “Fuji-1” blow-down facility are presented. In the experiment with Disk-F4 MHD generator, which was conducted with a modified seed injection system in 1997, an enthalpy extraction ratio of 18.4% was successfully demonstrated with a large output power of 506 kW. This enthalpy extraction ratio is the highest among those achieved with the Fuji-1 facility. The experimental results also revealed the electrical characteristics of the generator installed in the blow-down facility. The decline in the output power and its recovery were observed at the early stage of the power generation run. This fact could be attributed to the attachment of seed material to the generator walls and to its detachment, related to the relatively slow rise in temperature on the wall surface. It was verified for the first time in the Fuji-1 experiment that the reduction of impurity contamination resulted in improvement in the generator performance.

Micropipe defects and voids at β-SiC/Si(100) interfaces

Abstract The application of an uncommon silicon substrate pretreatment and a carbonization procedure without temperature ramp in a CVD reactor was found to create a new kind of defect besides the usual voids at β-SiC/Si(100) interfaces. SiC-covered micropipes of minute size and of high area densities evolve into the substrate by Si outdiffusion and simultaneous ingrowth of SiC. Results of our systematic investigations of micropipes and voids, obtained mainly by transmission electron microscopy (TEM), are summarized. The micropipe formation is obviously determined by very specific conditions such as, e.g., a high density of SiC nuclei at high carbonization temperatures. Recent new results demonstrate that micropipes together with voids can also develop in carbonization experiments during a relatively slow temperature rise at very low hydrocarbon concentrations.

Scanning thermal microscopy: Subsurface imaging, thermal mapping of polymer blends, and localized calorimetry

We have used a platinum/10% rhodium resistance thermal probe to image variations in thermal conductivity or diffusivity at micron resolution and to perform localized calorimetry. The probe is used as an active device that acts both as a highly localized heat source and detector; by generating and detecting evanescent temperature waves, we may control the maximum depth of sample that is imaged. Earlier work has shown that subsurface images of metal particles buried in a polymer matrix are consistent with computer simulations of heat flows and temperature profiles, predicting that a 1 μm radius probe in air will give a lateral resolution of ∼200 nm near the surface, with a depth detection of a few μm. We have a special interest in polymer blends, and we present zero-frequency mode and temperature-modulation mode thermal images of some immiscible blends in which the image contrast arises from differences in thermal conductivity/diffusivity between single polymer domains. The behavior of domains is observed in real time as the blends are subjected to a slow temperature rise. We have also achieved localized differential thermal analysis of a number of polymers, and recorded events such as glass transitions, meltings, recrystallizations, and thermal decomposition within volumes of material estimated at a few μm3. This opens the way forward towards calorimetric imaging, by which it should be possible to distinguish between different regions undergoing either reversible or irreversible changes as the temperature is varied.

Myocardial temperature response during radiofrequency catheter ablation.

During radiofrequency catheter ablation, steady-state electrode-tissue interface temperatures are reached within 5 seconds. Within the myocardium, however, a much slower temperature rise has been observed in vitro with stabilization after approximately 2 minutes. The discrepancy suggests that tissue temperature rise time depends on distance from the ablation electrode and, thus, that temperature rise measured at the electrode-tissue interface does not correspond with temperature rise within the myocardium. In five beagles, closed-chest radiofrequency catheter ablation was performed in the vicinity of intramural thermocouples. Sequences of 60 seconds, 10- and 25-watt pulses were delivered in the unipolar mode via the 4-mm distal electrode of a 7 French steerable catheter. At all distances > 3 mm from the ablation electrode, the rate of myocardial temperature rise was low: relative rise after 5, 10, 20, and 30 seconds was 22%, 32%, 48%, and 63% of that achieved at 60 seconds, and even then steady-state temperatures had not yet been reached. Temperature rise was faster at sites closer to the ablation electrode. There was no difference in rate of rise between first and second pulses at the same site. A 6% higher myocardial temperature was reached with a second identical pulse at the same site. Tissue temperatures achieved with 25 watts were 2.4 times higher than with a preceding 10-watt pulse at the same ablation site.

Temperature-controlled radiofrequency catheter ablation of AV conduction: first clinical experience.

A new technique for catheter ablation of atrioventricular (AV) conduction, using temperature-controlled radiofrequency energy and a bipolar asymmetrical electrode configuration, was applied to 12 patients (mean age, 48 +/- 15 years; range, 18-69 years) with medically refractory atrioventricular nodal reentrant tachycardia (AVNRT) or rapid atrial rhythms. The energy source was a 500 kHz generator with automatic power regulation to a preselected temperature of 80 degrees C. A specially designed 7 F bipolar asymmetric thermo-catheter was used for ablation in all cases. The endpoints of the procedure were: first-degree AV block in patients with AVNRT and third-degree block in patients with atrial fibrillation or flutter. Energy was applied over a range of 1-14 times per patient. After a mean follow-up of 8 +/- 4 months, third- or first-degree AV block persisted in eight patients. In comparison to constant-power radiofrequency ablation, where impedance rises are commonly observed, no impedance rise or coating of the electrode occurred during any of the 97 energy applications in this study. Variable wall contact of the electrode was identified in 20 of 97 applications by a slow temperature rise or a drop in temperature and frequent power adjustments. Thus, monitoring temperature and automatic power regulation may help to reduce the total delivered energy. Temperature control during radiofrequency energy avoids coagulum formation and consequently the associated potential hazards of constant-power application.

Ignition and extinction of a reaction in the presence of increasing external temperature: general results and slow temperature rise

We consider a homogeneous model for a first order, exothermic chemical reaction subjected to a linearly increasing external temperature. With u and v representing dimensionless internal temperature and concentration respectively, d u /d t ═ v exp [ u /( 1 + ∊ u )] – c ( u – βt ), d v /d t ═ – ∊ A v exp [ u /(1 + ∊ u )]. We examine the conditions under which the temperature u attains a local maximum and minimum, or alternatively is always increasing with time t .

Heat regulation during exercise with controlled cooling

During heavy sustained exercise, when sweating is usually needed to dissipate the extra metabolic heat, controlled cooling caused heat loss to match total heat production with little sweating. The total heat produced and metabolic rate were varied independently by having subjects walk uphill and down. Heat loss was measured directly with a suit calorimeter; other measurements included metabolic energy from respiratory gas exchange and body temperatures. Thermoregulatory sweating was minimized by adjusting cooling in the calorimeter suit. Heat loss rose to match total heat, not metabolic rate, and there was a slow rise in rectal temperature. In the absence of major thermoregulatory response rectal temperature correlated most closely with total heat; it also correlated with the relative oxygen cost of exercise. Heat flow or heat content appeared to be the controlled variable and body temperature rise a secondary event resulting from thermal transport lag.

Heat And Mass Transfer In An Intensely Heated Mortar Wall

This paper treats the diffusion-convection model of heat and mass transfer in a mortar wall under intense heating. Two features are taken into account for the generation of water vapor. The first one is the desorption of the physically adsorbed water in the pore, which causes the "Temperature Creep", slow temperature rise rate near 100'C. The second one is the thermal decomposition of crystalline water at higher temperature. The model is numerically solved for one dimensional case, and the results are shown for temperature, total pressure, partial pressure of vapor, physically adsorbed water content and crystalline water content. They show good agreements with the experiments.

Impulsive phase heating by uni-directional current systems in solar flares

The thermal interpretation of solar flare impulsive phase hard X-ray emission requires rapid heating of a substantial coronal volume to very high temperatures. In this study we investigate the possibility of producing such heating by current dissipation, driven by a tearing instability associated with a single uni-directional current system. Earlier research is synthesized by coupling the energy equation, including loss terms previously neglected, with an equation describing the evolution of the growing electric field. The resistivity due to the excitation of ion-cyclotron and ion-acoustic waves is computed by assuming marginal stability. It is found, for the fast tearing mode, that for initial growth rates γf≤ 0.3 s-1 (corresponding to a current channel width δl ≥ 3 × 105 cm), the electron heating is offset by convective losses, resulting in a very slow temperature rise. Furthermore, hard X-ray emitting temperatures (≈2 × 108 K) are never realized. For the larger growth rates corresponding to smaller current channel widths, heating from 107 to 108 K can be achieved in a few seconds. However, in this regime the maximum volume that can be heated is only of order 1020 cm3, some three to five orders of magnitude less than the volume of heated material that is inferred from hard X-ray emission measures. These results suggest that in the case of the fast tearing mode a more complicated geometry involving multiple small-scale, oppositely-directed, current channels may be necessary to achieve the required heating.

Hyperthermia-induced seizures with a servo system: Neurophysiological roles of age, temperature elevation rate and regional GABA content in the rat

A servo system including a microwave generator was applied to raise a rat's body temperature at a pre-set rate. Using this system the effects of age and the temperature elevation rate upon febrile seizures in rats were studied. The relationship between the brain GABA content and hyperthermia was also studied. From the results of the present study, the seizure occurrence rate was found to be highest at the age of 20 days, brain damage was speculated to be severe after hyperthermia-induced seizures with a slow temperature rise, and the regional GABA concentration in subcortical structures was found to increase during hyperthermia. These data indicate that a servo system with a microwave generator is useful for experimental febrile convulsions, and that GABA neurotransmission in subcortical structures might contribute to feed-back regulation against seizures during hyperthermia.

Combustion of Lean Flammable Mixtures in an Intense Radiation Field

A combustion process showing a slow temperature rise was realized in an intense radiation field by burning a lean combustible mixture in a refractory-lined cylindrical combustion chamber in which a permeable board was placed at the upstream and downstream ends, respectively. It was found by the measurement of the temperature and composition of gas along with the ion current and by high-speed schlieren photography that a laminar flame was attached to the lower part of the red-hot refractory surface and that it spread toward the top center, even if the mixture strength was below the lean flammable limit. The flame becomes convex toward the unburnt mixture due to some instability resulting in a kind of cellular structure. The flickering of the flame, due partly to the wavy motion of the flame base and partly to the cellular structure, is the cause of the slow temperature rise.

Transient hot spot temperatures at a sliding ceramic contact including surface coating effects

Prediction of hot spot temperatures at a sliding contact is important primarily from a wear viewpoint. The predictions are based on heat conduction models involving moving heat sources. In the present study, two new concepts are analyzed. The first concept is the prediction of transient hot spot temperatures with temperature-dependent properties (material and thermal) and time-dependent sliding speed. The solution of this non-linear problem with the data representing partially stabilized zirconia (PSZ) and Si 3N 4 indicates that the duration for the contact to reach 1000 °C was between 1 μs and 1 ms depending on the magnitude of the sliding speed. Accounting for thermal softening during the transient contact resulted in a slower temperature rise and lower peak values than those predicted by the constant hardness models. The contact area was shown to grow to twice its initial size due to thermal softening. The second concept analyzed is the effect of a surface layer on the transient hot spot temperatures. In this context, an equivalent resistance model is introduced which reduces the lengthy algebra usually associated with heat transfer modeling of layered solids. This model is used with the data representing a PSZ coating on a cast iron substrate. A PSZ coating on the order of 10 μm raised the steady hot spot temperature by an order of magnitude from what it would have been with a cast iron substrate alone. A thin PSZ film ( e.g. 0.05 μm), whose steady state effect was negligible, had a significant effect at the beginning of the transient.

Combustion of lean flammable mixtures in an intense radiation field.

A combustion process showing a slow temperature rise was realized in an intense radiation field by burning a lean combustible mixture in a cylindrical combustion chamber lined with a refractory in which a permeable plate was placed at the upstream and downstream ends, respectively. It was found by the measurement of the temperature and composition of gas along with the ion current and by high-speed schlieren photography, that a laminar flame was attached to the lower part of the red-hot refractory surface and that it spread towards the upper central portion, even if the mixture strength was below the lean flammable limit. The flame becomes convex toward the unburnt mixture due to some instability resulting in a kind of cellular structure. The flickering of the flame due to the wavy motion of the flame base and the cellular structure is the cause of the slow temperature rise.

Relationship between the characteristics of the menstrual cycle and congenital malformations in the human.

We have studied the characteristics of conceptional and pre-conceptional cycles in mothers of malformed infants. A comparison made with a control group of mothers of normal, term infants showed that for the former the hypothermic phase during the conceptional cycle was longer than for the latter (20.4 and 16.9 days, respectively). Moreover, the mothers of malformed infants showed a slower temperature rise (greater than 3 days) in 45% of cases, vs 28% in the controls. The menarche of the mothers of malformed infants occurs later (14.3 vs 12.8 years). They usually have long menstrual cycles and a bad obstetric and gynaecological history. The risk for congenital malformations is thus closely related to the length of the hypothermic phase and to a slow temperature rise in the conceptional cycle. Therefore we suggest that the preovulatory oocyte overripeness is one of the mechanisms of congenital malformation.